This answer to my question about light-as-a-weapon came up with an interesting concept:
This is a small African predatory bird with a perfectly smooth set of wings with an area of ~100 cm2, so maybe the size of a pigeon. It hunts in large flocks, around 10,000 birds to a group (there are plenty of real birds that form flocks this size).
Using some basic multiplication, this flock can focus about 130 kW of sunlight. The flock decides to kill and eat an elephant, who has a metabolism of around 3000 Watts and already has to work to keep cool on a warm day (heat sink ears, spraying water on itself, etc). By spreading out and focusing sunlight on the elephant, the birds totally overwhelm the elephant's ability to cool itself, raising its body temperature by about a degree Celsius every 2 minutes (130 kW / 4 tons*specific heat of water), leading to slow heatstroke and death. Divided evenly, there's a lb of meat for every bird in the flock, a huge windfall, sustaining the group though any cloudy days until the next kill.
I thought this was an intriguing idea as it nicely used light as a weapon in a novel and unexpected (and frankly terrifying) way. Imagine having a flock of these things decide you are their next lunch and start the slow cooking process...
The problem though is that while the end result is at least plausible, the evolutionary path is not obvious. How could a bird manage to evolve and become the Reflecting Oven Jay from a relatively normal starting point?